Question: $ D = \left[\begin{array}{rrr}2 & 2 & 2 \\ 2 & 0 & 0 \\ 1 & 1 & 0\end{array}\right]$ What is $ D^{-1}$ ?
Answer: $ = \left[\begin{array}{rrr}0 & \frac{1}{2} & 0 \\ 0 & -\frac{1}{2} & 1 \\ \frac{1}{2} & 0 & -1\end{array}\right]$